This disclosure relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in an example described below, more particularly provides for sealing off an annulus about a drill string with swellable materials.
In conventional drilling operations, a drilling fluid (also known to those skilled in the art as “mud”) is typically chosen to have a density which will prevent an influx of fluid from a formation being drilled. That is, hydrostatic pressure exerted by the drilling fluid is generally greater than pore pressure in the formation.
If, however, fluid from the formation should enter a wellbore, this can in some circumstances lead to an uncontrolled release of fluid from the wellbore. Therefore, it will be appreciated that it would be desirable to prevent, or at least reduce, such uncontrolled release of fluid from a wellbore.